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you'll hear the ticking...it should be a regular sound - not one valve out of the whole train...
the engine will always tick a little - but the ticking will just get a little more pronounced over time ....once every 20k or so you will need a valve adjustment...
Ticking will just tell you when your valves are too loose.Nothing tells you when they are too tight. If you can't find evidence of the valves ever being adjusted, I would do it now.